This is not an option in Mplus. You would need to create a data set with two variables, one for the factor loadings for sample one and the other for the factor loadings for sample two. Then you would need to estimate the correlation between these two variables to obtain the coefficient of congruence.

A more thorough way to do the analysis could be multiple group ESEM which is described in the Version 5.1 Examples Addendum which is available on the website with the user's guide.